1. Technical Field of the Invention
The embodiments of the invention relate generally to disk drives and, more particularly, to providing different defect processing to different portions of information read from a disk medium during a defect scan.
2. Description of Related Art
Varieties of memory storage devices, such as magnetic disk drives, are available to store data and are used to provide data storage for a host device, either directly, or through a network. Those networks may be a storage area network (SAN) or a network attached storage (NAS). Typical host devices include stand alone computer systems such as a desktop or laptop computer, enterprise storage devices such as servers, storage arrays such as a redundant array of independent disk (RAID) arrays, storage routers, storage switches and storage directors, and other consumer devices such as video game systems and digital video recorders. These devices generally provide high storage capacity in a cost effective manner.
One class of disk storage devices uses magnetic media to store information. In order to ensure that digital data is written to the disk and retrieved correctly, it is desirable to have defect-free media. However, manufacturing processes are not ideal and defects are introduced in the manufactured media. For example, one type of defect is caused by having a reduction of magnetic material on a medium below a specified value. Such reduction of magnetic material may cause a lower signal amplitude, which may result in a “dropout” condition. Alternatively, another type of defect is caused by having excess magnetic material on a medium above a specified value. Such increase of magnetic material may cause a higher signal amplitude, which may result in a “dropin” condition. Either defect condition may cause a bit or bits to be stored in an incorrect state when written to the medium and/or read incorrectly from the medium.
In order to address manufacturing defects of the types noted above, as well as other defects, a typical practice for disk manufacturers is to perform a defect scan to map defective sectors after the disk is manufactured. Generally, a defect scan entails writing a known test pattern on the disk, reading the stored bits and comparing the read bits to the known test pattern to determine sectors (or tracks) that contain defects. A defect mapping is then performed to identify those sectors (or tracks) that contain defects that are not acceptable. The defective sectors are then placed in a defect scan table and these sectors are not used for data storage when logical addresses are mapped to physical addresses on the disk to store data.
Although the above-described technique allows defect mapping to identify defective sectors (or tracks) on a medium, all scannable regions of the disk are treated the same, so that no differentiation is made between critical regions of a sector from less critical regions of the sector. For example, preamble and sync mark fields are generally regarded as more critical than user data fields, since user data may be further processed by an error correction mechanism, such as error correction code (ECC) to correct for errors. That is, more errors are generally tolerated with data fields, as compared to preamble and sync mark fields. However, no such distinction is made when the disk is scanned for defects. Depending on the defect threshold set for the scan, this uniform scanning technique results in 1) mapping out too many sectors on a disk drive, which may ultimately result in lower yield issues in the factory; or 2) having drive returns due to bad sync mark/preamble fields in which sectors are not mapped out when they should have been.
Accordingly, there is a need for another technique to perform a defect scan, in which different defect criteria may be set dependent on the type of information being read. By having different defect scan levels, critical regions of a disk may be treated differently from less critical regions when identifying the defects.